Jianfu Ding

Bulk heterojunction solar cells using thieno[3,4-c]pyrrole-4,6-dione and dithieno[3,2-b:2',3'-d]silole copolymer with a power conversion efficiency of 7.3%.

A new alternating copolymer of dithienosilole and thienopyrrole-4,6-dione (PDTSTPD) possesses both a low optical bandgap (1.73 eV) and a deep highest occupied molecular orbital energy level (5.57 eV). The introduction of branched alkyl chains to the dithienosilole unit was found to be critical for the improvement of the polymer solubility. When blended with PC(71)BM, PDTSTPD exhibited a power conversion efficiency of 7.3% on the photovoltaic devices with an active area of 1 cm(2).

Ice-phobic Coatings Based on Silicon-Oil-Infused Polydimethylsiloxane

A simple and low-cost technique for the preparation of silicon-oil-infused polydimethylsiloxane (PDMS) coatings with different silicon oil contents have been developed and studied. This material is designed for ice-phobic applications, and thus a high hydrophobic property of PDMS is maintained by avoiding any polar groups such as C═O and OH in the structure. Therefore, the polymer main chain was attached with vinyl and Si-H groups to obtain a cross-linking capability, meanwhile to ensure a nonpolar chemical structure. Its ice-phobic property has been investigated in terms of ice adhesion strength (tensile and shear), water contact angle, icing dynamics using high-speed photography and morphology using TEM, SEM and AFM. The prepared coating surface shows a low surface energy and very low ice adhesion strength of 50 kPa, only about 3% of the value on a bare aluminum (Al) surface. In the silicon oil infused PDMS coatings, the low surface energy of the silicon oil and PDMS, and the high mobility of silicon oil played an important role on the ice-phobic property. Both of these factors offer the surface a large water contact angle and hence a small contact area, leading to the formation of a loose ice layer. In addition, the oil infused polymer structure significantly reduces the contact area of the ice with solid substrate since the ice mostly contacts with the mobile oil. This leads to a very weak interaction between the substrate and ice, consequently significantly reduces the ice adhesion strength on the surface. Therefore, such material could be a good candidate for ice-phobic coatings on which the accumulated ice may be easily removed by a nature force, such as wind, gravity, and vibration.

Verification of Icephobic/Anti-icing Properties of a Superhydrophobic Surface

Four aluminum surfaces with wettability varied from superhydrophilic to superhydrophobic were prepared by combining an etching and a coating process. The surface wettability was checked in terms of water contact angle (CA) and sliding angle (SA) under different humidity at -10 °C. High-speed photography was applied to study water droplet impact dynamics on these surfaces. It was found that single and successive water droplets could rebound on the superhydrophobic surface and roll off at a tilt angle larger than 30° under an extremely condensing weather condition (-10 °C and relative humidity of 85-90%). In addition, the superhydrophobic surface showed a strong icephobic property, the ice adhesion on this surface was only 13% of that on the superhydrophilic surface, though they had a similar nano/microtopological structure. Moreover, this superhydrophobic surface displayed an excellent durability of the icephobic property. The ice adhesion only increased to 20% and 16% of that on the superhydrophobic surface after the surface was undergone 20 icing/ice-breaking cycles and 40 icing/ice-melting cycles, respectively. Surface profile and XPS studies on these surfaces indicated a minor damage of the surface nano/microstructure and the coating layer upon these multiple ice-breaking and ice-melting processes. Therefore, this superhydrophobic surface could be a good candidate for icephobic applications.

Development of a new s-tetrazine-based copolymer for efficient solar cells.

A new s-tetrazine-based low-bandgap semiconducting polymer, PCPDTTTz, was designed and synthesized. This is the first solution-processable conjugated polymer with tetrazine in the main chain. This polymer shows good thermal stability and broad absorption covering 450-700 nm. The HOMO and LUMO energy levels were estimated to be -5.34 and -3.48 eV, with an electrochemical bandgap of 1.86 eV. Simple polymer solar cells based on PCPDTTTz and PC(71)BM exhibit a calibrated power conversion efficiency of 5.4%.

Crystalline low band-gap alternating indolocarbazole and benzothiadiazole-cored oligothiophene copolymer for organic solar cell applications

A low band-gap alternating copolymer of indolocarbazole and benzothiadiazole-cored oligothiophene demonstrated balanced crystallinity and solubility; a solar cell combining this polymer with PC(61)BM in a preliminary test demonstrated power conversion efficiencies of 3.6%.

Synthesis and applications of difluorobenzothiadiazole based conjugated polymers for organic photovoltaics

A new electron deficient building block, difluorobenzothiadiazole (FBT) was designed and synthesized for the first time. Two low band gap polymers containing this unit or benzothiadiazole (BT) and an electron rich unit, benzo[1,2-b:4,5-b′]dithiophene (BDT) were synthesized by Stille coupling reaction. It was found that fluorine substitution significantly lowered the energy levels but did not affect the UV absorption properties of the polymer. Comparatively, the fluorinated polymer showed a higher melting point and a reduced solubility. The electrical and photovoltaic properties of these polymers were studied by fabricating thin film transistors and polymer solar cells. The solar cell based on FBT polymer and PC71BM gives power conversion efficiency up to 3.4% under AM 1.5 G illumination (100 mW cm−2).

Synthesis, characterization and photovoltaic applications of a low band gap polymer based on s-tetrazine and dithienosilole

A new copolymer of dithienosilole (DTS) and dithienyl-s-tetrazine (TTz), PDTSTTz, has been designed and synthesized. This solution processable polymer shows a low band gap, strong absorption and good thermal stability. Solar cells from the blend of this polymer with PC(71)BM showed power conversion efficiency (PCE) up to 4.2%.

Raman microscopy mapping for the purity assessment of chirality enriched carbon nanotube networks in thin-film transistors

With recent improvements in carbon nanotube separation methods, the accurate determination of residual metallic carbon nanotubes in a purified nanotube sample is important, particularly for those interested in using semiconducting single-walled carbon nanotubes (SWCNTs) in electronic device applications such as thin-film transistors (TFTs). This work demonstrates that Raman microscopy mapping is a powerful characterization tool for quantifying residual metallic carbon nanotubes present in highly enriched semiconducting nanotube networks. Raman mapping correlates well with absorption spectroscopy, yet it provides greater differentiation in purity. Electrical data from TFTs with channel lengths of 2.5 and 5 µm demonstrate the utility of the method. By comparing samples with nominal purities of 99.0% and 99.8%, a clear differentiation can be made when evaluating the current on/off ratio as a function of channel length, and thus the Raman mapping method provides a means to guide device fabrication by correlating SWCNT network density and purity with TFT channel scaling.

Low-threshold amplified spontaneous emission and laser emission in a polyfluorene derivative

The amplified spontaneous emission (ASE) and lasing properties of a fluorene copolymer PF3Cz film waveguide were investigated under optical pumping. Low ASE and lasing threshold were observed at 59 W/cm2/pulse and 1.7 KW/cm2/pulse, respectively. The stimulated emission cross section of the PF3Cz film was estimated to be approximately 1.6×10−16 cm2 at the ASE peak of 448 nm. The absorption cross section was estimated to be 2.8×10−16 cm2 at the absorption peak λ=370 nm. Gain and loss measurements at the ASE peak showed that the net gain coefficient reaches 26±1.7 cm−1 when pumped at 1.4 KW/cm2, and the loss coefficient of the waveguide was about 13±1.1 cm−1.

Preparation of Highly fluorinated poly(ether sulfone)s under mild polycondensation conditions using molecular sieves

Highly fluorinated poly(ether sulfone)s were prepared by a modified polycondensation technique, using a molecular sieve dehydrating apparatus in order to efficiently remove water under mild conditions. Consequently, side reactions were minimized, which resulted in the formation of polymers free of microgels. This reaction was also used to introduce pentafluorostyrene moieties into the polymer to provide crosslinking functionalities.